Blade Rub Material

ABSTRACT

One aspect of the disclosure involves a rub material comprising a polymeric matrix and polymer micro-balloon filler in the matrix. In one or more embodiments of any of the foregoing embodiments, the matrix comprises a silicone. In one or more embodiments of any of the foregoing embodiments, the rub material is at least I.0 mm thick. In one or more embodiments of any of the foregoing embodiments, the silicone is selected from the group consisting of dimethyl- and fluoro-silicone rubbers and their copolymers. In one or more embodiments of any of the foregoing embodiments, the micro-balloons at least locally have a concentration of 5-50% by volume.

BACKGROUND

The disclosure relates to blade rub coatings. More particularly, thedisclosure relates to abradable coatings for turbomachines such as gasturbine engines.

Abradable coatings (rub coatings) protect moving parts from damageduring rub interaction and wear to establish a mating surface to themoving parts with smallest possible clearance. The coatings are used inturbomachines to interface with the tips of a rotating blade stage, tipsof cantilevered vanes and knife edge seals.

In an exemplary turbomachine such as a gas turbine engine, moreparticularly, a turbofan engine, coatings may be used to interface withthe blade tips of fan blade stages, compressor blade stages, and turbineblade stages. Because temperature generally increases through the fanand compressor and is yet much higher in the turbine, different bladematerials, surrounding case materials, and coating materials may bedesired at different locations along the engine.

With relatively low temperatures in the fan and compressor sections,relatively low temperature materials may be used for their blades andthe surrounding cases (at least through upstream (lower pressure)portions of the compressor). The exemplary blade materials in such lowertemperature stages may be aluminum alloy, titanium alloy, carbon fiberor other composite, combinations thereof, and the like. Similarly,relatively lower temperature case materials may be provided.Particularly because the case material is not subject to the centrifugalloading that blades are, even lower temperature capability materials maybe used (e.g., aramid or other fiber composites) in the case than in theblades.

It is known to use a coating along the inboard or inner diameter (ID)surface of the case component to interface with the blade tips. Suchcoatings serve to protect blade tips from damage during rub contactbetween the blades and case. When the blade tips are protected fromdamage during rub, clearance between the blades and case ID can be setcloser and tighter operating clearance can be achieved.

To limit blade damage, the adjacent surfaces of the surrounding shroudmay be formed by an abradable rub coating. Examples of abradable rubcoatings are found in U.S. Pat. Nos. 3,575,427, 6,334,617, and8,020,875. One exemplary baseline coating comprises a silicone matrixwith glass micro-balloon filler. Without the glass filler, the elasticproperties of the abradable coating result in vibrational resonances andnon-uniform rub response. The glass increases the effective modulus ofthe coating so as to reduce deformation associated with aerodynamicforces and resonances.

SUMMARY

One aspect of the disclosure involves a rub material comprising apolymeric matrix and polymer micro-baloon filler in the matrix.

In one or more embodiments of any of the foregoing embodiments, thematrix comprises a silicone.

In one or more embodiments of any of the foregoing embodiments, the rubmaterial is at least 1.0 mm thick.

In one or more embodiments of any of the foregoing embodiments, thesilicone is selected from the group consisting of dimethyl- andfluoro-silicone rubbers and their copolymers.

In one or more embodiments of any of the foregoing embodiments, themicro-balloons at least locally have a concentration of 5-50% by volume.

In one or more embodiments of any of the foregoing embodiments, over adepth of at least 1 mm, the micro-balloons have said concentration of5-50% by volume.

In one or more embodiments of any of the foregoing embodiments, over adepth of at least 1 mm, the micro-balloons have said concentration of20-33% by volume.

In one or more embodiments of any of the foregoing embodiments, themicro-balloons have diameters of 10-80 micrometer.

In one or more embodiments of any of the foregoing embodiments, themicro-balloons have diameters of 20-45 micrometer.

In one or more embodiments of any of the foregoing embodiments, thematerial is injection molded in situ to a substrate or separatelyinjection molded and bonded to the substrate.

In one or more embodiments of any of the foregoing embodiments, thematerial of further comprises up to 50% by volume additional filler.

In one or more embodiments of any of the foregoing embodiments, thematerial of further comprises up to 50% by volume additional fillerselected from the group consisting of polymeric particulate filler,polymeric fiber filler, glass micro-balloons and combinations thereof.

Another aspect of the disclosure is a turbomachine comprising: aplurality of blades, each blade having a tip, the blades mounted forrotation about an axis; a case surrounding the plurality of blades andhaving: a substrate; and a coating of the blade rub material on thesubstrate facing the blade tips.

In one or more embodiments of any of the foregoing embodiments, theblades comprise an aluminum based substrate and a polyurethane coating.

In one or more embodiments of any of the foregoing embodiments, theturbomachine is a gas turbine engine wherein the plurality of blades area fan blade stage.

In one or more embodiments of any of the foregoing embodiments, theblades comprise an aluminum alloy or a titanium alloy.

Another aspect of the disclosure involves a blade rub segmentcomprising: a substrate; and a coating of the rub material of anyforegoing embodiment on the substrate.

In one or more embodiments of any of the foregoing embodiments, thesubstrate has a transversely concave first surface and an oppositesecond surface and a plurality of mounting features.

In one or more embodiments of any of the foregoing embodiments, thecoating has a transversely concave first surface and an opposite secondsurface secured to the substrate.

Another aspect of the disclosure involves a method for manufacturing thematerial of any of the foregoing embodiments, the method comprising:dispersing the micro-balloons in uncured polymer for the matrix materialby mixing.

In one or more embodiments of any of the foregoing embodiments, themicro-balloons are first dispersed in a solvent.

In one or more embodiments of any of the foregoing embodiments, themethod further comprises injection molding of the uncured polymer anddispersed micro-balloons.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially schematic half-sectional view of a turbofanengine.

FIG. 2 is an enlarged transverse cutaway view of a fan blade tip regionof the engine of FIG. 1 taken along line 2-2 and showing a first rubcoating.

FIG. 3 is a view of a blade rub segment.

FIG. 4 is longitudinal sectional view of a fan blade tip region of analternative engine.

FIG. 5 is an alternative enlarged transverse cutaway view of a fan bladetip region of the engine of FIG. 1 taken along line 2-2 and showing asecond rub coating.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

With a polyurethane coated airfoil, heat from rub friction conducts intothe airfoil causing a temperature rise which, in turn, causes thecoating to blister.

Thermal conductivity of the abradable coating material, size ofindividual filler particles/bodies, and temperature capability of fillermaterial influence heating of the airfoil. If the matrix or fillermaterial has low thermal conductivity, it will poorly conduct awaygenerated heat and airfoil temperatures would be higher than with anotherwise similar coating of greater thermal conductivity. Thetemperature capability of the coating material is defined as thetemperature at which the material decomposes, melts, or exhibits asubstantial drop in wear resistance when rubbed by a blade.

In the baseline coating (glass micro-balloon-filled silicone), becauseof machining of the coating during manufacture, or because of rub orerosion, the glass filler stands slightly proud of the polymer matrix.This results in preferential contact of the glass with the airfoil tips.Being of higher temperature capability than the polymer matrix, theglass filler undesirably allows the surface temperature during rub toreach a relatively higher temperature than if the polymer matrix werebeing rubbed. The extent of heating may approach the lower of themelting points of the glass and the mating aluminum blade. Not only doesthe glass filler produce a higher rub temperature, the hard phase(glass) particles increase the coating roughness after rub, reducingaerodynamic efficiency.

Use of thermoset polymer particles or micro-balloons (at least partiallyin place of baseline glass micro-balloons) may create a composite withsimilar bulk properties to the baseline material. However, it will limitthe maximum temperature at the rub contact to the maximum capability ofthe polymers. This will result in lower blade tip surface temperature,less heat input into the blade and lower temperature at the interfacebetween blade substrate and blade coating.

Abradable surface wear occurs during sliding contact of the blade tipagainst the abradable material. During contact the surfaces increase intemperature due to frictional heating. As the surfaces heat up during arub interaction, the rub forces are limited as the matrix and fillermaterials approach their temperature capability. This allows both thefiller and matrix to rub off during contact and allows the rub surfaceto adopt a profile that conforms to the shape of the blade path. With apolymer filler in the silicone matrix, the surface temperatures are thuslimited to the higher of the temperature capability of the matrix andthe filler. This temperature is in contrast to the temperature duringrub with low conductivity glass and mineral-based fillers of the priorart with which filler surface temperature may significantly exceed thecapability of the matrix. The maximum rub temperature is thus limited bythe temperature capability of the matrix and polymer filler.

Thus, replacement of glass filler with polymer filler reduces thetemperature capability of the composite and reduces the maximum rubtemperature. Lower temperature capability of the filler thus helps tolimit the maximum rub temperature by allowing the filler to wear away ata reduced temperature compared to glass micro-balloons.

Reduced temperature capability of the filler material reduces rubtemperature. Reduced rub temperature helps keep the blade tips cooler byreducing heat flux into the blades during rub. Reduced blade tiptemperature improves the durability of urethane erosion-resistantcoating on the airfoils.

FIG. 1 shows a gas turbine engine 20 having an engine case 22surrounding a centerline or central longitudinal axis 500. An exemplarygas turbine engine is a turbofan engine having a fan section 24including a fan 26 within a fan case 28. The exemplary engine includesan inlet 30 at an upstream end of the fan case receiving an inlet flowalong an inlet flowpath 520. The fan 26 has one or more stages 32 of fanblades. Downstream of the fan blades, the flowpath 520 splits into aninboard portion 522 being a core flowpath and passing through a core ofthe engine and an outboard portion 524 being a bypass flowpath exitingan outlet 34 of the fan case.

The core flowpath 522 proceeds downstream to an engine outlet 36 throughone or more compressor sections, a combustor, and one or more turbinesections. The exemplary engine has two axial compressor sections and twoaxial turbine sections, although other configurations are equallyapplicable. From upstream to downstream there is a low pressurecompressor section (LPC) 40, a high pressure compressor section (HPC)42, a combustor section 44, a high pressure turbine section (HPT) 46,and a low pressure turbine section (LPT) 48. Each of the LPC, HPC, HPT,and LPT comprises one or more stages of blades which may be interspersedwith one or more stages of stator vanes.

In the exemplary engine, the blade stages of the LPC and LPT are part ofa low pressure spool mounted for rotation about the axis 500. Theexemplary low pressure spool includes a shaft (low pressure shaft) 50which couples the blade stages of the LPT to those of the LPC and allowsthe LPT to drive rotation of the LPC. In the exemplary engine, the shaft50 also drives the fan. In the exemplary implementation, the fan isdriven via a transmission (not shown, e.g., a fan gear drive system suchas an epicyclic transmission) to allow the fan to rotate at a lowerspeed than the low pressure shaft.

The exemplary engine further includes a high pressure shaft 52 mountedfor rotation about the axis 500 and coupling the blade stages of the HPTto those of the HPC to allow the HPT to drive rotation of the HPC. Inthe combustor 44, fuel is introduced to compressed air from the HPC andcombusted to produce a high pressure gas which, in turn, is expanded inthe turbine sections to extract energy and drive rotation of therespective turbine sections and their associated compressor sections (toprovide the compressed air to the combustor) and fan.

FIG. 2 shows a cutaway blade 100 showing a blade substrate (e.g., analuminum alloy) 102 and a polymeric coating 104 (e.g., apolyurethane-based coating) on the substrate. The exemplary coating isalong pressure and suction sides and spans the entire lateral surface ofthe blade between the leading edge and trailing edge. The exemplarycoating, however, is not on the blade tip 106. If originally applied tothe tip, the coating may have been essentially worn off during rub.Circumferential movement in a direction 530 is schematically shown.

FIG. 2 also shows an overall structure of the fan case facing the blade.This may include, in at least one example, a structural case 120. It mayalso include a multi-layer liner assembly 122. An inboard layer of theliner assembly may be formed by a rub material 124. The exemplary rubmaterial 124 has an inboard/inner diameter (ID) surface 126 facing theblade tips and positioned to potentially rub with such tips duringtransient or other conditions.

As is discussed further below, the rub material 124 comprises apolymeric matrix material 128 and a polymeric filler 130. The exemplaryrub material may be formed as a coating on an ID surface 132 of asubstrate 134 of the liner assembly. An exemplary substrate 134 istitanium alloy AMS 4911. The rub material is shown as having an overallthickness T_(R). Exemplary T_(R) is 1-10 mm, more particularly, 3-6 mm.

The matrix material may initially be an uncured rubber such as a liquidsilicone rubber (e.g., family including liquid dimethyl- andfluoro-silicone rubbers and their copolymers). The silicone rubber isprocessed as a liquid and cross-links with time and temperature to forma thermoset solid material. Exemplary matrix material is RTV630 ofMomentive Performance Materials Inc., Columbus Ohio.

Exemplary polymeric filler is present in the rub material at an overallconcentration of about 25% by volume, more broadly 20-33% or 5-50%. Thismay be an overall average or a local average (e.g., if concentrated in adepth zone (e.g., at least 1 mm or at least 2 mm) near the surface).

Exemplary filler is polymer micro-balloons to reduce coating density andimprove abradability. Exemplary micro-balloons are acrylonitrile such asDuolite E030 acrylonitrile micro-balloons produced by HenkelCorporation, West Haven, Conn. Exemplary balloon diameter is 20-45micrometer (more broadly, 5-150 micrometer or 10-80 micrometer).

The coating may be manufactured by mechanical mixing of themicro-balloons with the uncured silicone (e.g., in an extruder). Thecoating may be applied by injection molding (e.g., directly to thesubstrate or separately followed by adhesive bonding to the substrate).Alternative material may be formed in sheets (e.g., by extrusion) andthen cut and bonded for installation.

FIG. 3 shows a rub strip segment 160 including a segment 161 of thesubstrate 134 and a segment of the rub material 124. The exemplarysegment 160 is dimensioned for use in a fan case 150 (FIG. 4, e.g.,itself of a two-piece circumferential segmentation) of a low-bypassmilitary-style turbofan engine. An exemplary 4-20 (more narrowly 6-12)such segments 160 may be assembled to form an annulus circumscribing theengine axis. The substrate segment may be formed as a metallic carrierhaving a main body with a forward edge 162, a rear edge 164, and firstand second circumferential edges 166 and 168. Mounting features 170(e.g., hooks such as shown or studs, clips, sockets or the like) may bepositioned at leading and/or trailing ends or the outer diameter (OD)surface 172 of the body for mounting to complementary features (e.g.,rails 152) of the case 150. The ID surface 132 is the ID surface of thebody and is transversely concave to match blade sweep. In alternateimplementations of such a low-bypass engine, the coating may be moldeddirectly to the fan case substrate (e.g. of a horizontally-split case).

The segment of rub material may have a planform generally coextensivewith the planform of the substrate main body. For example, the rubmaterial segment 180 may have a forward edge 182, a rear edge 184, andfirst and second circumferential edges 186 and 188, each slightly proudof the corresponding substrate main body features. This allows thesubstrate segments to be spaced slightly apart from each other whileallowing snug mating of the rub material segments with each other. Italso has an outer diameter (OD) surface 190 along and secured to the IDsurface 132.

In an original use situation, a virgin substrate may be manufacturedsuch as by machining (if metallic) or by molding or composite lay-up orother technique, whereafter the rub material may be applied.

After molding, the rub material may be machined, if not molded directlyto size, to establish desired dimensions of the surface adjacent to theairfoils and to establish desired clearances at engine build. The rubmaterial may be machined on the individual segments, split case halves,assembled in a fixture as a full circle or in an engine sub-assembly (helast being known as an “assembly grind”). Exemplary machining of theabradable material is by grinding, single point turning, or milling.

In remanufacture situations, after at least partial consumption of therub material, the remaining rub material may be removed (e.g.,mechanically, chemically, and/or thermally). Exemplary mechanicalprocesses include any of the manufacturing machining processes orpreferably by water jet strip if the substrate is metallic and cansurvive the water jet process. A new body of rub material may then beovermolded to the cleaned substrate.

The potential benefits from reducing the temperature capability of thefiller used in a silicone rubber abradable coating are not limited tocoating consisting of rubber-polymer microballoon composites. Thus, thecomposites may contain other components (e.g., fillers andreinforcements). The benefit of reducing the maximum temperature at therub interface also exists in fiber-reinforced and solid particle-filledabradables. Solid particle polymer fillers such as polyethyle (PE),polymethylmethacrylate (PMMA), acrylonitrile copolymer, etc. have lowertemperature capability than glass and mineral fillers and result inlower blade tip temperature. Among such fillers are those disclosed inU.S. Pat. No. 6,334,617 mentioned above and the disclosure of which isincorporated herein by reference in its entirety as if set forth atlength. Additionally, fiber reinforcements such as carbon nanotubes andpolyester may be added to further modify the mechanical properties ofthe matrix. Exemplary concentrations of polymeric particulate and fiberfillers are in the range of up to 50% by volume overall, moreparticularly up to 20% or up to 33% or 5-33% or 10-20% by volume,whereas the carbon nanotube fiber reinforcement concentration is in therange of 1-33% by volume in the matrix (e.g., as first blended into thematrix prior to adding micro-balloons) or more ideally 5-15% by volumein the matrix. Exemplary combined concentration of the polymericmicro-balloons and other filler is up to 60% by volume, more narrowly,up to 50% or 20-40%.

One particular example of a beneficial abradable composition useschopped polyester fibers 140 (FIG. 5) to reduce coating density andimprove tear resistance and visio-elastic damping properties to keep thematerial stable during rub abradability. Exemplary concentration of suchfibers is ˜5% by weight overall or ˜8% by weight relative to the matrix.

One or more embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made. For example, whenapplied in the redesign of a baseline engine configuration or for theremanufacturing of a baseline engine, details of the baseline willinfluence details of any particular implementation. Accordingly, otherembodiments are within the scope of the following claims.

1. A rub material (124) comprising: a polymeric matrix (128); andpolymeric micro-balloons (130) and 5-33% by volume additional filler(140) in the matrix.
 2. The material of claim 1 wherein: the matrix(128) comprises a silicone.
 3. The material of claim 1 wherein: the rubmaterial is at least 1.0 mm thick.
 4. The material of claim 2 wherein:the silicone is selected from the group consisting of dimethyl- andfluoro-silicone rubbers and their copolymers.
 5. The material of claim 1wherein: the micro-balloons (130) at least locally have a concentrationof 5-50% by volume.
 6. The material of claim 5 wherein: over a depth ofat least 1 mm, the micro-balloons (130) have said concentration of 5-50%by volume.
 7. The material of claim 5 wherein: over a depth of at least1 mm, the micro-balloons (130) have said concentration of 20-33% byvolume.
 8. The material of claim 1 wherein: the micro-balloons (130)have diameters of 10-80 micrometer.
 9. The material of claim 1 wherein:the additional filler comprises polymeric fiber at 5-33% by volume. 10.The material of claim 1 injection molded in situ to a substrate (134) orseparately injection molded and bonded to the substrate.
 11. Thematerial of claim 1 comprising: 10-20% by volume said additional filler(140).
 12. The material of claim 1 wherein: said additional filler (140)is selected from the group consisting of polymeric particulate filler,polymeric fiber filler, glass micro-balloons and combinations thereof.13. A turbomachine (20) comprising: a plurality of blades (100), eachblade having a tip, the blades mounted for rotation about an axis; acase (28) surrounding the plurality of blades and having: a substrate(134); and a coating of the blade rub material (124) of claim 1 on thesubstrate facing the blade tips.
 14. The turbomachine of claim 13wherein: the blades comprise an aluminum-based substrate (102) and apolyurethane coating (104).
 15. (canceled)
 16. (canceled)
 17. A bladerub segment (160) comprising: a substrate (134); and a coating of therub material (124) of claim 1 on the substrate.
 18. The blade rubsegment of claim 17 wherein: the substrate has a transversely concavefirst surface (132) and an opposite second surface (172) and a pluralityof mounting features (170).
 19. The blade rub segment of claim 17wherein: the coating has a transversely concave first surface (126) andan opposite second surface (190) secured to the substrate.
 20. A methodfor manufacturing the material of claim 1, the method comprising:dispersing the micro-balloons in uncured polymer for the matrix materialby mixing.
 21. The method of claim 20 wherein: the micro-balloons arefirst dispersed in a solvent.
 22. The method of claim 20 furthercomprising: injection molding of the uncured polymer and dispersedmicro-balloons.
 23. (canceled)